Topographic Degradation Processes of Lunar Crater Walls Inferred from Boulder Falls

Abstract

Recent explorations by lunar orbiters have shown that boulder falls are distributed over the entire lunar surface. To quantitatively evaluate the effects of moonquakes and meteorite impacts on boulder falls, we performed detailed surveys at two sites: one in the southern part of the Schrödinger basin (Site 1) and the other in Laue crater (Site 2). Using images and topography data fromthe Lunar Reconnaissance Orbiterand KAGUYA, we estimated the detailed distributions of boulder falls, small craters, slope angles, the optical maturity parameter (OMAT), and maximum acceleration due to impacts at these sites. In steeply sloping areas at both sites, we found that the density of small craters was small and areas with high OMAT values corresponded to boulder sources, where many boulders exist. At Site 1, the starting points of boulder falls and acceleration due to impacts were correlated. In addition, craters with boulder falls at and around Site 2 were distributed independently of the epicentral distance from a shallow moonquake that occurred in 1975 near Site 2, which was previously inferred to have triggered boulder falls at the site. Our results suggest that boulder falls at these sites were triggered not by moonquakes but by meteorite impacts. We propose a model for the generation and transport of boulders and regolith on slopes by meteorite impacts, which may be directly related to the degradation of crater slopes on the Moon.

Timing and Origin of Compressional Tectonism in Mare Tranquillitatis

“…The evidence includes for both landforms (Figure 1), the abundance of boulder fields and patches (French et al., 2019; Valantinas & Schultz, 2020; Watters et al., 2019), a distinct crisp morphology (e.g., Watters et al., 2010; Williams et al., 2019), crosscutting of impact craters (Lu et al., 2019; Nypaver & Thomson, 2022; Watters et al., 2010), ages <1 Ga determined from CSFD methods (Lu et al., 2019; Valantinas et al., 2018; van der Bogert et al., 2018), shallow moonquakes (Watters et al., 2019), boulder falls (Senthil Kumar et al., 2016), and associated small meter‐scaled graben (French et al., 2015; Valantinas & Schultz, 2020; Watters et al., 2012). The correlation between boulder falls and seismic activity, however, has been questioned recently (Bickel et al., 2021; Ikeda et al., 2022), highlighting the ongoing and early state of the study of recent tectonic activity. Late‐stage global contraction is consistent with both an initially molten Moon (Binder & Gunga, 1985; Watters et al., 2019) and a near‐surface magma ocean (Solomon, 1986; Solomon & Head, 1979; Watters et al., 2019), however, the magnitude of the late‐stage stresses predicted in the totally molten Moon model is inconsistent with the population of small lobate thrust fault scarps (Watters et al., 2012, 2015).…”

Topographic Degradation Processes of Lunar Crater Walls Inferred From Boulder Falls

“…The MI and DEM data are available at https://darts.isas.jaxa.jp/planet/pdap/selene/product_search.html by entering "SELENE MOON MI 5 MAP V3.0" and "SELENE MOON TC 5 DTM MAP SEAMLESS V2.0" into the "Data set name" field, respectively, with latitude and longitude ranges shown in the image names in Table S1 in Supporting Information S1. Our estimated data of small craters, boulder trails, and boulder sources, densities of small craters, and OMAT values are available in Ikeda et al (2022).…”

“…Our estimated data of small craters, boulder trails, and boulder sources, densities of small craters, and OMAT values are available in Ikeda et al. (2022).…”